1. Field of the Invention
The present invention relates to mechanical devices providing rhythmic action. More particularly, the invention relates to fluid control circuits providing rhythmic action for sequential compression devices, such as circulatory assist devices.
2. Description of the Related Art Various examples of fluid control circuits for sequential compression devices used to assist patients in circulating fluid around a limb or limbs are provided by U.S. Pat. Nos. 4,396,010 (to Arkans), 4,481,937 (to Arkans) and U.S. Pat. No. 4,858,596 (to Kolstedt). The contents of these patents are incorporated by reference herein as background material.
Prior art fluid control circuits utilize a series of valves and pressure relief valves, which must be periodically opened and closed, for circulating the liquid through a sleeve or cuff. Opening and closing of the valves requires either a series of solenoid controls (with sophisticated electronic controls) or cam actuators. The hardware necessary for the control of opening and closing valves uses large amounts of power and increases the bulk of such devices.
In addition, the mechanical action of the valves, solenoids and cams are prone to wear and tear, which will degrade the quality of the compression device over time, requiring high costs for maintenance and repair. Thus, there exists a need in the art for improvement in fluid control circuits.
One of the present inventors previously designed a valve-less artificial heart utilizing a dual fluid oscillator (U.S. Pat. No. 3,599,244, the content of which is incorporated by reference herein as background material), which relies on the dynamic flow properties of blood for its operation. In this device, the system provides better reliability than prior art artificial hearts using mechanical valves, which often fail.
However, the dual fluid oscillator of the prior art requires the placement of a pump at each output having a pressure, which is directly related to the input pressure, and is inversely related to the pressure head against which it is being pumped. Moreover, the fluid from one part of the dual fluid oscillator does not directly transfer the fluid to the second (or any other) oscillator, as would be required in a sequential compression device.
Finally, the prior art dual fluid oscillator also requires that the oscillator portions must be arranged contiguously with each other so that a filling of a first fluid oscillator with a working fluid increases the pressure to such a level that the pressure against a common diaphragm causes the diaphragm to press against the second fluid oscillator, emptying the second fluid oscillator.